In a time-of-flight mass spectrometer (which is hereinafter called the “TOF-MS”), a fixed amount of kinetic energy is imparted to ions, which are derived from a sample component, entering an ion acceleration region positioned at an entry port of a mass separator to make those ions fly a specific distance within a flight space and determine the mass-to-charge ratio of each ion from its time of flight.
A system of imparting the kinetic energy to the ions in the time-of-flight mass spectrometer includes an orthogonal acceleration (which may also be called “vertical acceleration” or “orthogonal extraction”) system. In the orthogonal acceleration TOF-MS, ions entering the ion acceleration region (orthogonal acceleration unit) are introduced to the flight space while being accelerated in a direction orthogonal to its entering direction, and allowed to fly therein. Therefore, the ions can be analyzed with a high mass-resolving power without being influenced by a variation in flight speed (energy) of the ions introduced in the orthogonal acceleration unit (for example, see Patent Literature 1).
FIG. 1(a) illustrates an example of a schematic configuration of a mass separator 100 of an orthogonal acceleration reflectron TOF-MS.
Ions ejected from a prior stage (lower part of FIG. 1(a)) of the mass separator 100 enter an ion acceleration region of orthogonal acceleration electrodes 102 (formed of a pair of electrodes 102A and 102B arranged to face each other, where the electrode 102B is a grid electrode), and are accelerated in a direction orthogonal to the entering direction (toward the grid electrode 102B). The ions passing through the grid electrode 102B are further accelerated by acceleration electrodes (second acceleration electrodes) 103 arranged on both sides of an ion trajectory, and are incident into a flight space of which the outer end is defined by a flight tube 104. The ions incident into the flight space are gradually decelerated after being incident into a space formed by reflectron electrodes 105 and a back plate 106, and then, the ions are incident into a detector 107 along its returned flight path.
In order that the ions flying toward the flight space from the orthogonal acceleration electrodes 102 are made to fly along such a trajectory, voltages with an appropriate magnitude are applied to the second acceleration electrodes 103, the flight tube 104, the reflectron electrodes 105, and the back plate 106 to form a potential having a gradient decreasing toward the flight tube 104 from the second acceleration electrodes 103 and increasing toward the reflectron electrodes 105 and the back plate 106 from the flight tube 104, as illustrated in FIG. 1(b).
FIG. 2 is an example of an electrode circuit of a voltage application device for applying voltages to the second acceleration electrodes 103, the flight tube 104, the reflectron electrodes 105, and the back plate 106. In the electrode circuit, a plurality of resistances are connected in series between two power sources P1 and P4 at both ends, an electrode connection part is arranged between neighboring resistances, and power sources P2 and P3 are also connected at two different locations intermediate the both ends.
Between the power source P1 and the power source P2, four electrode connection parts and three resistances Ra are alternately provided. The three electrode connection parts closer to the power source P1 are connected to the second acceleration electrodes 103, and the electrode connection part closer to the power source P2 is connected to the flight tube 104, respectively.
Between the power source P2 and the power source P3, the three electrode connection parts and the two resistances Rc are alternately provided, and the three electrode connection parts are connected to the front side reflectron electrodes 105a. 
Between the power source P3 and the power source P4, the four resistances Re and the four electrode connection parts are alternately provided. The three electrode connection parts closer to the power source P3 are connected to a rear side reflectron electrodes 105b, and the electrode connection part closer to the power source P4 is connected to the back plate 106, respectively.
It is noted that the power source P3 is connected via a resistance Rd to the electrode circuit.
From each of the power sources P1 to P4, a voltage is outputted having a polarity (the same polarity as the ions or an opposite polarity to the ions) according to the polarity of an ion to be measured, and having a magnitude according to a potential formed in each unit. For example, during positive ion analysis, a voltage of V1 (for example, −3 kV), a voltage of V2 (for example, −7 kV), a voltage of V3 (for example, +2 kV), and a voltage of V4 (for example, +2 kV) are output from the power sources P1 to P4, respectively (first state). During negative ion analysis, the polarity of the output voltage of each of the power sources P1 to P4 is reversed (second state). When the positive ions and the negative ions generated from a sample are measured in turn, the positive ions are firstly measured in the first state, and then, the first state is switched to the second state where the negative ions are measured.